Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon.
The semiconductor industry continues to improve the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by continual reductions in minimum feature size, which allow more components to be integrated into a given area. These smaller electronic components also require smaller packages that utilize less area than packages of the past, in some applications.
One smaller type of packaging for semiconductors is a flip chip (FC) ball grill array (BGA) package, in which semiconductor die are placed upside-down on a substrate and bonded to the substrate using micro-bumps. The substrate has wiring routed to connect the micro-bumps on the die to contact pads on the substrate that have a larger footprint. An array of solder balls is formed on the opposite side of the substrate and is used to electrically connect the packaged die to an end application.
However, some FC-BGA packages tend to exhibit bending, where warping of the substrate occurs during processing due to temperature stress, such as in solder flow processes which can have temperature ranges from about 240 to 260 degrees C. The warping results from coefficient of thermal expansion (CTE) mismatches in various material layers and components of the package and die. The substrate expansion is typically larger than that of the die, for example. Such warping and bending can cause reliability issues, lower assembly yields, bond breakage or shorts, and cold joints of the micro-bumps. Warpage behavior is more of a problem with thin core package substrates and can range from convex warpage at room temperature to concave warpage at high temperature, for example.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.